1. Field of the Invention
The present invention relates to a camera system that has a data communication function between the camera body and the photographing lens.
2. Description of Related Art
In a recent single lens reflex camera having an automatic focusing device, information peculiar to a photographing lens, such as open F-number data used in an automatic exposure function or an automatic focusing function is sent as electrical signals from the photographing lens to a CPU (central processing unit) of the camera body.
Information peculiar to the photographing lens is stored in a lens ROM provided in the photographing lens. The photographing lens and the camera body are provided with electrical contacts on a lens mount and a body mount to transmit and receive the signal information between the photographing lens and the camera body, respectively. The body CPU transmits and receives the signal information to and from the lens ROM through the electrical contacts and reads the data stored in the lens ROM. A clock pulse is output from the camera body to send address signals from the body CPU synchronously therewith, so that predetermined data can be output from the lens ROM in accordance with the address signals.
Furthermore, in a single lens reflex camera with a photographing lens having an AF motor (automatic focusing motor) and a PZ motor (power zoom motor), etc., if the control of these motors is effected by the body CPU, there is an over load on the body CPU. In particular, in a single lens reflex camera in which various kinds of photographing lenses are exchangeably mounted to one camera body, the body CPU must read different parameters, depending on the photographing lenses from the associated lens ROM's, and perform predetermined arithmetic operations in accordance with the read parameters to control the photographing lenses. This makes quick operation impossible or next to impossible.
In addition to the foregoing, various data, including a drive pulse coefficient K value which is the number of pulses (conversion coefficient) in accordance with a lens movement distance per unit defocus amount in an automatic focus control of a zoom lens, etc., are stored in the ROM of the photographing lens. Therefore, a large part of the memory of the ROM is used for that data. Accordingly, the stored data must be partially erased or a large capacity ROM must be used instead of a conventional ROM to write new data.